oil spill models, such as those developed and run by the National Oceanic and 

 Atmospheric Administration and the U.S. Coast Guard for response to real time 

 spills (Wallops Workshop 1980). 



OIL SPILL RISK MODEL 



1. Overview 



The DOI oil spill risk model is one of the largest environmental models in 

 current use; larger models are used by the National Weather Service. The 

 overall workings of the model are discussed by Smith et al. (1982). Detailed 

 documentation of the model is presented by Lanfear and Nakassis (1980) and 

 Lanfear and Samuels (1981). A brief overview of the model with examples of 

 lease sale applications is presented by Lanfear et al. (1970). Model runs for 

 each OCS lease sale, beginning in 1976, are described and results presented in 

 the USGS Open File Report series; recent examples, for Southern California and 

 the Gulf of Mexico, are presented by Samuels et al . (1981a) and LaBelle and 

 Samuels (1981), respectively. 



For a specific application the region to be modeled is defined based upon 

 the locations of potential spill sites (production and transportation), locations 

 of potentially vulnerable resources, and knowledge of winds and currents which 

 characterize the region. Typically the modeled region includes 600 to 800 nmi 

 of coastline and extends seaward about 400 nmi. 



The model is structured on a grid (480 x 480). All spatial information are 

 digitized and portrayed on the model grid. Computer programs are incorporated 

 to allow input data to be on virtually any map projection and map scale. 

 Digitized inputs include the shoreline, ocean currents, and locations of 

 biological resources. Hypothetical oil spills are launched from potential 

 spill sites and advected within the model grid by wind and current. Spill 

 contacts with various "targets" are recorded along with the time between spill 

 launch and contact. Spills are launched throughout the year and in sufficient 

 numbers to establish statistical significance to the contact probabilities. 



Contact probabilities derived in this fashion are conditional in that spill 

 occurrence is assumed. The conditional probabilities are then combined with 

 the likelihood of spill occurrence to yield the final (joint) probabilities 

 that spills will occur and will contact specific targets. 



2. Salient Points 



The oil spill risk model is well documented in the published literature. 

 In addition, as noted above, there are published reports describing each sale 

 specific model run. Thus, I attempt here to summarize selected topics. The 

 topics were chosen to reflect the capabilities of the model. The topics 

 discussed below are intended to also represent the collection of issues most 

 frequently raised by the public who interact with the OCS Program. 



The model deals with oil only on the ocean surface. Spills, represented by 

 points (hypothetical center of mass of a surface slick), are advected by surface 

 currents and winds. The surface currents are climato logical (generally average 



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